hey guys,
i already posted this in the blitz black thread, bult i figured i'd make a new thread in to see if anyone could give me some tips. I just painted my fairlane with john deer blitz black paint, i mixed it 8:1 with the john deer reducer, and i sprayed it early in the morning so it was still cool out so the metal wasn't hot. Also, i sprayed it with a vaper (takoff on sata i guess, everyone i've talked to said they're great guns so i'm assuming that a bad gun isn't my problem) hvlp gun set at 15 psi, with a 1.4 tip. But, after it dried the paint looks like one big giant orange peel, kind of like the paint got sprayed in droplets. It's over the entire car and not only a few areas. I know it's not because of the john deer paint because i sprayed my door jambs with a rattle can of the same stuff and it turned out awesome. Do i have the gun set wrong? or is an hvlp gun not good to spray an enamel with? Any advice would be appreciated, i have no problem scuffing the whole car again and respraying, if i can't get the john deer stuff to work i'll just go with some ppg black primer, what do you guys think i should do? thanks a lot

Being HVLP and low VOC products are the way the industry’s going I will be referring to them in this discussion on painting and paint guns. Most all basic issues dealing with HVLP can be applied to conventional guns, atomization is atomization. The HVLP just arrives at it differently.

The object of the spray gun is to break up the primer/sealer/paint/clear (I will call this “PSPC” from here out) into small particles and lay them in neat little rows on the panel being PSPRed. So the whole outcome rests on how well the gun is doing this. Picture the droplets of PSPC coming out of the fluid tip of the gun and then the air “slapping” them into smaller droplets.

You have two things that help you with this process, air and solvent. Solvent can mean something that is already in the PSPR from the manufacture or something the manufacture has told you to add to it. By the way, you should always mix in proper ratios as instructed in the tech sheet. The thinner (less viscosity) you get the PSPR or the more air you have at the fluid tip of the gun the more it will break up the PSPR. The target for you is getting the perfect balance needed. Too much solvent and the PSPR will have no body, fill, durability, etc. Too much air and you blow the PSPR everywhere but the car, poor adhesion, excessive texture, etc.

So, the answer is proper air supply and gun (and fluid tip) choice and how you adjust it.

With today’s high solids-low VOC (Volatile Organic Compound, you know the bad stuff that goes up into the air we breathe) products there is less solvent. And with HVLP guns there is less air at the cap to break up the PSPC, proper air supply and gun setup is more important than ever.

FIRST THINGS FIRST, your compressor and air supply.

An HVLP gun requires more VOLUME of air to operate (the V in HVLP, High Volume Low Pressure). Now you may notice that your HVLP gun is adjusted at maybe the same PSI as an old conventional gun, around 50 lbs at the gun (many HVLP guns are set at much lower though) so where is the “Low” in PSI they are talking about? It is at the actual air cap where the air and paint come out. An HVLP gun has only 10 lbs at the cap while a conventional has upwards of 50! So the VOLUME of air (CFM, Cubic Feet per Minute) is the key to proper atomization with an HVLP.

This 10 lbs I am mentioning is AT THE CAP where the air and paint comes out. It is not measurable without a special air cap that has a gauge built in to it. This air cap costs about $150.00 (and you would need a different one for every brand and model of gun you use) and is not needed to set up or tune your gun. Just looking at the droplet patterns will tell you everything you need. I only refer to it to make a point about HVLP operation.

If you have a gun that requires 15 CFM you will need a compressor and plumbing that will produce that at a very minimum. There are HVLP guns that need as little as 7.5 CFM so you can get good results even from a smaller compressor. Air supply is a complete subject by it’s self so lets assume that you have the air supply needed and move on to gun set up.

So atomization is the key, but why? Why can’t you just lay it out wet and let it “flow”, as an old painter will say. Picture a jar full of bb’s, they will represent well small, atomized droplets of PSPC. The gaps in between the bb’s is solvent. Now picture a jar filled with marbles, they will represent large, poorly atomized droplets of PSPC. The gaps in between are, you guessed it, solvent.

If you apply your PSPC in large poorly atomized droplets, what you will have is a film full of solvent. This can and will cause slow curing, shrinkage and dieback (the loss of gloss in the hours and days after application).

So, now that we have learned the need for gun set up, how do we do it? Lets start with the fluid tip choice. The newer high solids low VOC PSPC products need to be broken up more, so a smaller fluid tip is needed.
Basically you want the smallest fluid tip that will still allow you to PSPC the particular part you are PSPCing keeping the entire thing wet and in a fair amount of time. In other words a 1.0 tip would be beautiful for clearing one fender, but would be lousy to paint a complete. The application would be way to slow and the first panel would be way to flashed by the time you got around back to it. So you need to compromise, a 1.3 is a great all around tip, while a 1.5 though getting a little big, can get you by. If you read the tech sheet on the particular product you are shooting, it will have a recommendation for fluid tip size.
There are needs for other tips, for instance when shooting polyester primer you may need as big as a 2.3, but for urethanes and epoxies, the 1.3 or 1.4 will work great. If you plan on using a pressure pot or paint a bus, all bets are off and we would need to study a little bit more.

As an example of the use of a 1.3 tip I did a test once that proved the point well. I shot two panels of metal with a med solids urethane primer. One was shot with a 1.3 super high atomizing top of the line topcoat gun. The other was shot with a 1.5 (or a 1.7 I can’t remember) “hoser” primer gun. Three coats were applied and after a full cure (the one shot with the larger gun took MUCH longer to flash and cure by the way) the film thickness was measured. The one shot with the 1.3 tip was 2 tenths of a MIL thicker! The larger gun laid out the marble sized droplets full of solvent and when the solvent flashed the film shrank.

Air supply is a subject that could fill many pages by it’s self. So we are going to assume you have that covered and move on to gun set up.

You need to “tune” your gun EVERY TIME you use it just as you would tune a guitar before you perform. This is done with a very basic spray out pattern test. This very basic test tells you how your gun is atomizing and you adjust it to achieve the best atomization you can.

Lets do a spray pattern test:

Set the fan width as need (you don’t want to change it after you have “tuned” the gun). Turn out the material knob about 2 ˝ turns. This is the “mixture” adjustment, kind of like the idle screw on a carburetor. The farther in it is screwed the lower the fluid to air ratio is and the smaller the droplets will be. The farther out it is, the higher the fluid to air ratio is and the larger the droplets.
Set the air pressure at the inlet to the gun to the manufactures specs. On an HVLP gun this spec is usually found on the gun and is the maximum PSI it can have while still maintaining the maximum 10 lb at the cap for legal HVLP transfer efficiency (68 %). You are now ready to do a test spray out.

Tape a piece of masking paper on the wall for the test. Hold the gun at a right angle to the wall, just as if you were going the wall. Hold the gun at a spread out hands distance (about 8” or 22cm). Pull the trigger to completely open for a split second and then close it. You want an ON-OFF wide open-completely closed in ONE movement. You should have a cigar shaped pattern with complete coverage in the center with fading coverage going away from the full coverage cigar shape in the center. The center should be fully covered without any runs. If you have runs, either you are holding the trigger too long, you are too close or the gun is simply applying too much material. In which case you need to screw in the material knob or turn the air pressure down. But most likely if you have turned the material knob out the 2 ˝ turns and the air is set at the factory specs, you are just too close or holding the trigger open too long.

The droplets you see trailing off the center are what you will use to “tune” your gun.

Turn in the material knob to make the droplets smaller (and or raise the air pressure). The balance you need to attain is the smallest droplet size possible before you loose the coverage desired. In other words if you turn in the material knob too far, not enough material will be coming out to cover the panel!

Now, you’ll notice that I said, “raise the pressure to the gun”, while earlier I said to set it to manufactures specs. We are talking a very small adjustment. It is a fine balance in material to air ratio and a little more air than specified is okay. Even if it is an HVLP gun the inlet pressure recommended is to maintain the 10 lb limit at the cap. Well, about three quarters of the country has no regulations for HVLP use so if you go over the 10 lbs all it will do is atomize the material a little better. You may loose a little of the benefits of HVLP though. But remember you have a lot of control with the material adjustment knob.

After you are happy with the droplet size, DON’T TOUCH THE FAN CONTROL. It will change the PSI at the cap and will change the atomization you worked hard to get.
Do this spray out every time you spray as material change, temp, and humidity will necessitate a spray out droplet pattern test. Good luck!
Click here to see a sprayout pattern

hey guys, thanks a bunch for the replies, bondoking that writeup from martinsr is great. tomorrow i'm going to play with the gun and see if i can get it to spray better, it does sound like my air pressure was way too low. I'll let you guys know how it goes, thanks again!

hey badbob,
thanks for the advice! i sanded a fender today, with a da and 220 grit paper and it worked alright, didn't really ball up on me. i played aroudn with the settings on the gun and turned the pressure WAY up and it shoots nice now so i'll test it on the fender i sanded down and if it's nice, sand and reshoot the car. i'll let you guys know how it goes.

I actually ran at around 48 PSI when shooting JDBB, laid flat, turned out beautiful. One question for you, did you use the JD Buff Primer??? That sure helps. Also the 8:1 rule didn't work out to well on my test panel, I think I was 6:1, laid one coat med-wet, then 2 more coats heavy. No peel and it is tough as nails.

hey jeeptuff,
wow that's a lot of pressure, i was afraid to turn it up that hight, i had it at about 30 and it was spraying a lot better, i'll turn it up some more today and see how it goes! i used the buff primer in spots where i did body work or where it was bare metal, but everywhere else i used the existing paint and just scuffed it since it was in good shape and scuffed real smooth. Do you have any pictures? I'll shoot some more test panels today at around 48 psi and with the 6:1, thanks a bunch for the advice.

ok i painted my fender this morning with the paint reduced 6:1 and the pressure at 45, it layed down smooth. but now, it's shiny on my bronco i have ppg black bc/cc job and the fender is just as shiny as that, what did i do!? the whole reason i wanted the blitz black was to be shinier than primer, but not even close to as shiny as bc/cc, or even a normal gloss black enamel. i was going for the suede look. did i lay the paint on too thick or something? Thanks a lot guys, help me out!

here's a picture i got of the fresh painted fender next to the old painted hood, you can see how much shinier it is, i'm going to keep experimenting today with it and see if i can dull it down a little

Hey flamedfordbronco, it has been years since we shot this but it does not come along very often when someone wants a matt finish. Most folks want it to shine like it is wet. But there was a clear coat we shot over a shiny finish to make it a matt finish. I wish i could remember the name and brand, but sorry. I am sure it is still out there somewhere. That was back before the EPA forced us to use differant kinds of paint. Whatever it was callled, it gave us a finish similar to the hood in the photo where you showed us the fender and hood.

personally it looks to me like you put your clear on waaayy to thin! spraping clear is much different then base coat. the gun needs to move slower aand go over it 2 times slow in one coat it will be good!

well air presure sounds way low. kick presure up too about 30-35 . as far as setting material ajustment back nob way out sqeeze trigger then start turnin nob back with trigger sqeezed tight when you feel fluid needle pressing on trigger turn nob one and ahalf more time and never jack wit it again. you control material bye feathering trigger. nock offs can work but they take alittle more skill than the real thing.

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